1. Field of Invention
This invention relates to an elevator for bulk material, and related apparatuses, in particular but not exclusively for use in harvesting machines, grain silos and hoppers.
2. Background of Prior Art
An example of the mass flow or bulk flow of so-called xe2x80x9cbulk materialxe2x80x9d is the flow of grain to the grain tank in a combine harvester. It is known to provide a flow meter that operates by measuring forces of this flow on a sensor surface. Such flow meters may also be employed in hoppers, silos, harvesting and cutting machinery other than combine harvesters, conveying machinery and various kinds of manufacturing and medical apparatuses.
Bulk flow may also embrace, e.g. the flow of bulk grain and chemicals in transport vehicles (such as tankers, ships and railway tanker wagons); the flow of e.g. powders, and materials of larger particle size such as fruit, vegetables, coal, minerals and ores; and even the flow of liquids of high viscosity. Thus the invention may be of use in the elevating of liquids whose viscosity changes over time. In general terms, bulk flow of material may in this context be regarded as any flow of matter in contact with a surface, in which the effects of friction between the surface and the material usually influence the maximum flow rate, and in which the matter exhibits free flow behaviour.
U.S. Pat. No. 5,959,218 includes a discussion of the applications of mass flow meters, for measuring the mass flow rate of bulk materials, in the combine harvester art; and also a discussion of some prior art mass flow meters. The entire description of U.S. Pat. No. 5,959,218 is incorporated herein by reference.
The arrangement of U.S. Pat. No. 5,959,218 is a highly successful apparatus for measuring the mass flow rate of grains in a combine harvester, without reducing or interrupting the flow of grains. The invention seeks to provide additional advantages over those arising from mass flow meters such as, but not limited to, the U.S. Pat. No. 5,959,218 arrangements and methods.
In a combine harvester the grain elevator lifts grain between the grain cleaner and the bubble up auger that in turn transfers the grain to the grain tank. As a result of use of a combine harvester during a harvesting season, the chain defining a major part of the grain elevator stretches and slackens.
The chain is usually an endless ovaloid or similar shape that is wrapped at its lower and upper ends around, respectively, a drive sprocket (at the lower end of the elevator) and a tensioning (driven) sprocket (at the upper end of the elevator). It is therefore conventional to include a releasably securable mounting, for the tensioning sprocket, that is position adjustable e.g. in a direction parallel to the elongate axis of the ovaloid. The combine harvester operator or service engineer may release the mounting in order to take up slack in the chain, by repositioning the tensioning sprocket; and then re-secure the mounting.
The elevator chain supports a series of elevator paddles that move with the chain during operation of the elevator. The paddles pick up grain at the base of the elevator, convey it to the top thereof and then, by virtue of the loci of the paddles (that are dictated in turn by the shape of the chain) throw the grains outwardly at the top of the elevator. The trajectories of the grains are constrained by the interior walls of a hollow, concave elevator head that encloses the otherwise open upper end of the elevator.
The elevator head guides the grains to a bubble up auger that conveys the grains to the clean grain tank of the combine harvester.
In the flow path of the grains between the elevator and the bubble up auger it is known to install the sensor surface of a mass flow measuring device (meter) as disclosed in U.S. Pat. No. 5,952,584 or U.S. Pat. No. 5,959,218. Typically the walls of the elevator head act as a lead-in guide surface for guiding the grains into contact with the sensor surface.
The loci of the elevator paddles is arcuate in the vicinity of the top of the grain elevator. The top wall of the elevator head is generally of complementary shape to the loci of the paddles in this region. Consequently the spacing between the free edges of the paddles and the said wall is substantially constant, at least over a certain length of the top wall.
A proportion of the grain conveyed by the paddles falls through the gap between the paddle ends and the elevator head top wall. As a result of re-tensioning of the elevator chain in the manner aforesaid, this gap diminishes. Consequently the proportion of the grain falling off the paddles via the spacing after re-tensioning also diminishes, with the result that grain flows at a more controlled speed onto the sensor surface, than before the re-tensioning operation, because the grain is influenced less by grain moisture content or kernel size.
Such a reduction in the proportion of grain falling off the conveyor paddles causes a greater proportion of the conveyed grain to impact the sensor surface of the mass flow measuring device at a controlled speed. This in turn increases the average speed at which the grain reaches the sensor surface.
The mass flow measuring device is calibrated in part on the assumption that the grains will impact the sensor surface at a known speed. Clearly the aforementioned change in average speed of the grains invalidates the assumption and thereby reduces the accuracy of the mass flow measuring device following chain re-tensioning.
According to a first aspect of the invention, there is provided an elevator for bulk material having a hollow, upwardly extending elevator housing having respective lower and upper openings and substantially enclosing an endless, flexible conveyor for conveying bulk material. The bulk material entering the housing at the lower opening, to the upper opening. The elevator including a head assembly having a plurality of members secured together to define a hollow, rigid closure that closes the upper opening of the elevator housing. The elevator head supporting within the hollow, rigid closure a guide surface for guiding bulk material in the elevator head. The elevator head also includes supported within the hollow, rigid closure a sensor surface of a mass flow measuring device, towards which the guide surface guides bulk material following its elevation by the said conveyor and a rotatable drive transfer assembly for rotatably engaging and tensioning the flexible conveyor.
The elevator head includes a lever member extending laterally of the elevator beyond the sensor surface. The lever member being pivotably secured to a fulcrum that is fixed relative to the elevator housing, whereby on pivoting of the lever member about the fulcrum the elevator head and the components supported thereby move together. This permits adjustment of the tension in the conveyor without substantially altering the positions of the conveyor, the guide surface and the sensor surface relative to one another.
An advantage of this arrangement is that the gap between the paddle free edges and the elevator head does not change as a result of a chain re-tensioning operation. Consequently the accuracy of the mass flow measuring device is maintained.
Preferably the endless, flexible conveyor includes an endless chain supporting a series of bulk material elevator paddles that lift bulk material from the lower opening and project it towards the sensor surface at the said upper opening, the chain defining an upwardly extending ovaloid path of the said conveyor and being wrapped at the lower and upper ends of the ovaloid respectively around a drive sprocket; and
a tensioning sprocket that constitutes the said rotatable drive transfer assembly, whereby, on upward pivoting of the elevator head, the tensioning sprocket increases the tension in the chain. These features advantageously suit the elevator of the invention to use in a combine harvester.
In preferred embodiments the elevator head includes a mounting door supporting a mass flow measuring device, the mounting door openably closing an aperture in the elevator head and including a perforation and having rigidly secured thereto a mass flow measuring device a component of which extends through the perforation whereby the sensor surface of the mass flow measuring device is supported within the said hollow, rigid closure; and the remainder of the mass flow measuring device is supported externally of the hollow, rigid closure. This arrangement advantageously ensures that only the sensor surface of the mass flow measuring device is exposed to the harsh environment within the elevator head.
The mounting door may preferably be pivotably secured to the elevator head whereby the door is moveable between a closed position in which the sensor surface lies within the hollow, rigid closure and an open position in which the sensor surface lies substantially or entirely outside the hollow, rigid closure. This configuration permits ready access to the sensor surface of the mass flow measuring device, for cleaning and maintenance such as replacement of a liner plate secured to the sensor member to define the sensor surface proper.
In particularly preferred embodiments the elevator includes a releasable detent for releasably securing the mounting door in its closed position. This is a simple, robust means of retaining the mounting door in its closed position.
The mass flow measuring device may take any of a number of different forms. One preferred form includes a rigid anchor member that is rigidly secured to the elevator head, a rigid mounting member having rigidly secured thereto a sensor surface assembly, a resiliently deformable connection; and a load cell connected in series in a load transferring circuit.
This form of measuring device is conveniently compact. The resiliently deformable connection and the load cell confer flexibility on an otherwise substantially rigid structure. Since there are two flexible components in the load transferring circuit the overall stiffness of the device may be controlled, by selecting the stiffness of the resiliently deformable connection and the load cell respectively.
Conveniently one part of the load cell is secured to the anchor member and the mass flow measuring device includes a rigid link interconnecting a further part of the load cell and the mounting member. Preferably the load cell and the rigid link pre-tension the resiliently deformable connection.
This advantageously ensures that even when no grain is flowing on the sensor surface the mass flow measuring device produces an output signal. This in turn facilitates the elimination of drift from the output of the measuring device at zero grain flow.
In the preferred form of mass flow measuring device the resiliently deformable connection and the load cell include respective axes of deformation that are non-coinciding in use of the grain elevator. This ensures that the stiffnesses of the load cell and resiliently deformable connection are additive, thereby assuring operation of the measuring device.
In the presently most preferred form of the mass flow measuring device the anchor member includes a through-going aperture and the rigid link extends through the said aperture to interconnect the load cell and the mounting member. This arrangement of components significantly assists in conferring compactness on the device.
Conveniently the anchor member, the resiliently deformable connection and the mounting member are formed integrally one with another. One way of achieving this configuration is to machine the anchor member, the resiliently deformable connection and the mounting member from a single block of a preferred metal.
The integral nature of the aforementioned components provides a pivot that is not substantially susceptible to the deleterious effects of wear and contamination with e.g. dust and grease. Also the natural frequency of the resiliently deformable connection may be carefully controlled during manufacture of the device. This is highly advantageous because for example the interior of a combine harvester is subject to significant vibration. The ability to tune the natural frequency of the resiliently deformable connection during manufacture helps to eliminate noise, arising from such vibration, from the resulting mass flow signal generated by the load cell.
In the preferred form of the mass flow measuring device the resiliently deformable connection functions as a pivot about which the moment generated by the force of grains on the sensor surface acts. For high sensitivity of the device the stiffness of the resiliently deformable connection is less than the stiffness of the load cell.
The sensor surface assembly of the mass flow measuring device preferably includes at least one rigid sensor support rigidly secured to the mounting member and extending therefrom to one side of the resiliently deformable connection; and a sensor member, including a sensor surface, secured to the sensor support, whereby the bulk flow of material on the sensor surface causes deflection of the resiliently deformable connection and the load cell.
Such a sensor support is conveniently sturdy and compact; and possesses a high natural frequency, thereby assisting to eliminate spurious vibrations from the output signal of the mass flow measuring device.
When the elevator includes a mounting door as aforesaid the or each sensor support extends through a through-going aperture in the mounting door, whereby in use of the elevator the sensor member lies on one side of the mounting door within the hollow closure; and substantially the remainder of the mass flow measuring device is spaced therefrom by the mounting door.
This advantageously allows only the sensor surface to be exposed to the harsh environment inside the elevator head.
In one form of the mass flow measuring device the or each sensor support additionally extends on the opposite side of the resiliently deformable connection, and has secured thereto a counterbalance mass counterbalancing the mass of the sensor member. This advantageously allows the moment contributed by the mass flow measuring device to be substantially zero, thereby permitting greater accuracy and ease of signal processing.
When the grain is projected from the elevator onto the sensor surface the grain flow tends to spread. Before the flow reaches the end of the sensor plate it tends to reach the side edges of the plate. Consequently the total flow is not detected by the measuring device over the entire length of the sensor surface.
The location and the amount of grain that flows off the sensor plate along the sides is dependent on the mass flow, crop type, moisture content of the grain and the slope of the machine on the sensor is mounted. These parameters can vary a lot in the conditions where the machine (such as a combine harvester) has to work.
Therefore a further, optional feature of the elevator head according to the invention is the inclusion in the hollow, rigid closure of a pair of mutually parallel sidewalls, that are spaced from one another to define the lateral boundaries of part of the travel of each said conveyor, opposed portions of said sidewalls being thickened in the vicinity of the trajectory of the projected bulk material. This arrangement avoids the aforementioned problem of the spreading of flow on the sensor surface.
A further, preferred feature of the sidewalls of the sensor surface includes thickening of the said opposed portions by plates of substantially the same shape and dimensions as the said opposed sidewall portions and secured to the said opposed sidewall portions. Conveniently the said lateral edges of the said sensor surface include protruding therefrom a plurality of walls that define boundaries to the lateral travel of bulk material on the sensor surface; and the plurality of walls are a pair of flat, parallel, mutually spaced walls upstanding from respective, opposed lateral edges of at least part of the sensor surface.
An alternative arrangement involves use of a chute of part-toroidal shape (i.e. a curved chute of semi-circular cross-section). This shape may avoid potential material build-up that could arise at the junction of a straight, upstanding wall with a flat sensor surface. However, the latter kind of sensor surface is simple to manufacture.
The invention is also considered to reside in a combine harvester including an elevator, as defined herein, located for elevating grain within the combine harvester.
In a particularly preferred form of combine harvester according to the invention the lever member of the elevator extends into the grain tank of the combine harvester, whereby the said fulcrum also lies in the said grain tank.